The present invention relates generally to clevis joints, and more specifically, to zero free play pin clevis joints for deployable space structures. 2. Description of the Related Art
Deployable truss structures have myriad uses in outer space, such as the construction of space stations, platforms, etc. A multibay deployable truss structure may have hundreds of pin clevis-type joints that must move with low friction for the truss to deploy reliably.
Pin clevis joints are generally known and usually include a U-shaped shackle attached to an end of a structural member and having its ends drilled to receive a cylindrical pin or bolt. A projecting shank or tang provided at the end of another structural member is provided with a hole usually of the same diameter as the drilled portion of the U-shaped shackle. The tang is then inserted between opposite sides of the shackle such that when the hole in the tang is aligned with the drilled portion of the shackle, the pin passes through the shackle and tang to unite the two ends of the structural members.
Pin clevis-type joints used in deployable space structures have a problem associated with clearance between the pin and the clevis holes. This clearance leads to free-play in the joint. A deployable truss structure having hundreds of pin clevis-type joints experiences an accumulation of free-play along its length. Free-play degrades the ability to position the structure accurately, and makes structural stiffness difficult or impossible to predict. These conditions can make surface control and position control impossible using conventional sensors and controls.
As an example of the difficulty required in fabricating space-quality deployable beam hardware, an 18-bay deployable beam structure was fabricated by NASA for laboratory test purposes. The beam had over 375 pin clevis-type joints. To alleviate the problem of joint free-play, the pins and holes of the joints were machined to tolerances in the range of 0.0002 inches, and the pins were hand picked to match the hole size and pressed into the joint members. Therefore, the existing solution to the free-play problem is expensive and highly labor intensive, and therefore, impractical.
The problem of free-play is critical in space applications and other applications involving precision machinery in which zero free play is required, such as precision robotic machines. However, the problem is most critical to space structures which require multiple joints, in which free-play, which may be very slight in one joint, is multiplied perhaps several hundred times.